Riders of the Bay Area's commuter rail system may still have to find alternative means of getting to work Tuesday if no labor agreement is reached by midnight.

Users of the Bay Area Rapid Transit system were spared from a shutdown at the last minute Sunday night after union leaders agreed to extend negotiations for one more day. But they made it clear workers would be walking off the job if no agreement is reached by midnight, affecting some 200,000 riders.

Emerging from a marathon session of negotiating, Antoinette Bryant, president of the Amalgamated Transit Union Local 1555, told reporters Sunday night that the final offer from management was "regressive" and inadequate.

After agreeing to a one-day extension for talks, she was adamant that the strike would commence at 12:01 a.m. Tuesday if no deal was reached.

Amalgamated Transit and Service Employees International Union Local 1021 represents 2,375 mechanics, custodians, station agents, clerical workers and train operators.

“We will ensure that our passengers, who we care deeply about, get to where they need to go at the end of the day," Bryant said, adding that "we regret that this action has to happen."

BART General Manager Grace Crunican issued a statement just before midnight Sunday saying the final management offer included a 12% raise over four years and represented a $7-million boost over Friday's offer. The unions have two weeks to vote on the "last, best and final" offer, she said.

"It is time to bring this to a close," she said. "The Bay Area is tired of going to bed at night and not knowing if BART will be open or not."

The 12% raise would be below union demands of more than 20% in early summer.

The failure to achieve a deal by the midnight deadline was somewhat unexpected, as both unions and management had indicated over the weekend that the trajectory of talks was positive.

Lt. Gov. Gavin Newsom, speaking outside California Department of Transportation headquarters earlier Sunday, said failure to reach agreement would be “preposterous for both sides at this stage, when you’re getting this close, to put at risk your reputation and the economy of the entire region. Everyone loses.”